How does Chip Kelly decide what to do on fourth down? "Just by the feel of the game," Kelly said Thursday. (AP)

It's the first drive of the season.

The Eagles were at Washington's 24: third-and-4, 13:33 on the game clock.

LeSean McCoy ran for three yards, got up, and the clock read 13:27.

Now it's fourth-and-1 on the Redskins' 21.

The Eagles could kick a 39-yard field goal or go for it. Teams in this situation often do one of two things. They run up to the line and call a QB sneak. Or they call timeout to discuss their options. (Or, as Grantland's Brian Barnwell pointed out in his fourth-down analysis, some head coaches panic and make a bad call.)

What did the Eagles do?

The ref spotted the ball, the Eagles lined up, center Jason Kelce surveyed the defense, and he put his hand on the ball with 13:11 on the clock.

The ball was snapped two seconds later. Michael Vick handed off to McCoy, who ran up the middle for four yards.

First down. Time between plays: 18 seconds.

"You can get an advantage one or two ways," Kelce said. "You can call a timeout and get really good personnel on the field that you think you can take advantage of, or you can rush it and try and catch them off guard a little bit, and we decided to do that that way."

That's normally the reasoning behind running the sneak, and when a defense sees a team rushing to the line for a fourth-and-short, it probably expects it. But head coach Chip Kelly was ready with more than a sneak. A step ahead, he was ready in case Shady fell a yard short. When a defense sees the Eagles hustle to the line on fourth down, it won't know what to expect. It's just like any other down.

"Everybody's got the quarterback sneak in their package where they just run up right away and try and catch the defense off-guard a little bit," Kelce said. "The difference with us is that since we're used to going up-tempo and used to going so fast, it's not just the quarterback sneak. We have a number of plays we can get to very quickly."

And the Redskins had little time to prepare for any of them. First, they had only 18 seconds to catch their breath. Second, because there was so little time to sub, they couldn't bring in fresh players or players more suited for short yardage.

"That's the beauty of tempo," right tackle Lane Johnson said. "We run so many plays so fast, they can't get adjusted and can't get the right personnel on the field to cover it all."

Going for it on fourth down is nothing new for Kelly, who made a habit of it at Oregon and did so by going with his gut.

"Just by the feel of the game," Kelly said. "I've never dealt with the odds and the percentages and you get .21 if you go for it and the risk is 68 percent and your field goal kicker -- that's way too much math for me."

The bottom line is this: The Eagles still had to execute. Regardless of how much time the Eagles take between plays, if they don't make plays, all this up-tempo stuff is moot.

"I think when people take time on fourth down and they don't convert it, everybody says the reason you didn't convert it is because you took time," Kelly said. "If we had gone fast and didn't execute our blocks, then people would say, ‘You didn't execute it because you went too fast.’

"A lot of times it comes down to, it's not how fast you do it or how slow you do it. You still have to block the people. It's still a game of fundamentals and do we do a good job of executing what we called better than they do a job of executing what they called."